In recent years, more and more electronic devices, such as mobile phones, are provided with a touch sensor that detects contact by a user. There are many known systems for detecting contact, such as a resistive film system and a capacitive system. All of these systems detect contact by a contacting object such as the user's finger or a stylus pen.
There are also electronic devices that, in addition to the front surface, also include a touch sensor on the back surface. For example, JP 2012-230567 A (PTL 1) discloses a mobile terminal that includes two touch sensors, one on the front surface and one on the back surface, and that based on a predetermined correspondence relationship associated with the usage state, accepts input to a first back surface or a second back surface as input to a first front surface or a second front surface, thereby increasing user-friendliness.